TECHNOLOGY CORE SUMMARY The two primary goals of this Center are to build a whole brain transcriptome atlas and a more detailed forebrain cell anatomy atlas. These goals will be achieved by three Research Segments that will be supported and enhanced by transcriptomic technologies and pipelines developed and refined in the Technology Core. The Core's functions will be managed by the lead Dr. Anthony Zador (CSHL), and supported by co-leads Drs. Evan Macosko (Broad Institute) and Edward Boyden (MIT). First, we will optimize and integrate MAPseq and Drop-seq for high-throughput projection mapping of molecular classified neurons. MAPseq (Multiplexed Analysis of Projections by Sequencing) is a novel technology developed by the Zador laboratory with the capacity to determine the long-range projections of thousands or even millions of single neurons in a single experiment. The combination of MAPseq and Drop-seq has the potential to relate projection patterns with transcriptomes at an unprecedented scale. Second, we will integrate MAPseq with in situ sequencing to determine the long-range projections of neurons whose spatial position and molecular identity is precisely determined. This technique offers significantly improved spatial resolution over using MAPseq alone, and will enable rapid and affordable brain-wide survey of gene expression and projection with high spatial resolution. Optimization of the throughput, resolution, and cost efficiency of these techniques in the Technology Core will complement and enhance the goals of this Center and those of the BRAIN initiative cell census network to define the composition of the mammalian brain at the cellular level.